SMA STILL ON GND FREQ BUT BELIEVES ON TWR. THINKS HE HAS CLRNC TAXI POS AND HOLD.

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I RECEIVED CLRNC TO TAXI TO RUNUP AREA FOR RWY 29 ON GND FREQ. I TAXIED TO RUNUP AREA; ACCOMPLISHED MY RUNUP. SAN JOSE REQUIRES YOU TO CALL GND WHEN YOUR RUNUP IS COMPLETED AND NOTIFY THEM YOU ARE READY TO TKOF. I THEN RECEIVED INSTRUCTIONS TO CALL TWR AND TAXI UP TO THE HOLDING AREA OF RWY 29. I HAVE RADIOS WHICH HAVE FLIP- FLOP FREQ SELECTION. I HIT THE BUTTON TO SWITCH TO TWR; HOWEVER; IT DID NOT SWITCH OVER AND I DID NOT CATCH IT. I THEN CALLED WHAT I THOUGHT WAS THE TWR; BUT WAS STILL ON GND FREQ; AND TOLD THEM I WAS #1 FOR RWY 29. THIS IS WHERE THE PROBLEM AROSE. THERE WERE 3 OR 4 AIRLINERS WAITING FOR TKOF AND SEVERAL OTHERS CALLED FOR PUSHBACK. THE GND FREQ WAS VERY BUSY. THE BASIC PROBLEM WAS THAT I HEARD A REPLY ON GND FREQ WHICH WAS PARTIALLY STEPPED ON BY THE OTHER ACFT THAT SOUNDED TO ME LIKE 'TAXI IN POS ON RWY 29.' I ONLY CAUGHT 'RWY 29.' SINCE I WAS #1 AND AFTER CHKING FOR LNDG TFC I TAXIED ONTO RWY 29 AND HELD. I WAS STILL ON GND FREQ AND AFTER ABOUT 10 SECONDS; GND CTL TOLD ME I WAS STILL ON GND AND TO GO TO TWR FREQ. IT WAS THEN THAT I REALIZED I WAS STILL ON GND FREQ. I HAD ERRED IN SWITCHING OVER AND TAXIING ONTO THE RWY WITHOUT BEING ON TWR FREQ. SAN JOSE IS A HUB FOR AN AIRLINE AND IS VERY CONGESTED ON GND FREQ. THEY COULD USE ANOTHER GND FREQ -- 1 FOR EACH SIDE OF THE ARPT. TRUE; I ERRED IN NOT DOUBLECHKING MY RADIO FREQ; HOWEVER; IT WAS COMPOUNDED BY THE CONGESTED GND FREQ. IT COULD BE JUST AS EASY FOR AN AIRLINER TO DO THE SAME THING.